Microporous alumina membranes electrochemically grown

The electrochemical fabrication of alumina membranes by anodizing of aluminium in phosphoric acid and oxalic acid solutions, in the temperature interval from -1 to 16 degreesC, was investigated in order to Study the influence of different parameters (initial treatment of aluminium surface, nature and composition of electrolyte, temperature) on the final characteristics of the membranes. Porous layers were grown using a linear potential scan at 0.2 V s(-1) up to 160 V in H3PO4 solution and 70 V in oxalic acid solution. The efficiency of porous layer formation was calculated by using Faraday's law and weight measurements. Pore size distribution and porosity of membranes prepared in 0.4 M H3PO4 were found to be dependent on temperature, while in 0.04 M smaller pore size and lower porosity were obtained, independent of temperature. Highly ordered structures were formed by aluminium anodizing in 0.15 M oxalic acid solution at 70 V. A uniform pore diameter of about 90 nm was found, independent of temperature. A porosity value of about 26% was achieved and it was found to be independent of temperature for membranes prepared in oxalic acid. Porous layers grown either in H3PO4 or oxalic acid solution crystallized at temperatures around 870-890 degreesC. For membranes formed in oxalic acid the pyrolysis of oxalate anions also occurs. (C) 2003 Elsevier Ltd. All rights reserved.